1. Field of the Invention
The present invention relates generally to rotating machines such as electric motors and generators and, more particularly, to electric motors and generators having a current-carrying stator with an induced current in a rotating inner rotor with coolant passing through the current carrying portion of the rotor.
2. Prior Art
There have been many proposals intended to improve the operation of transducers for electrical power/mechanical power conversion (motors or generators). However, there are still areas where the use of electric motors remains impractical, for example for use as the main drive of a vehicle such as a car. Current electric motors are generally too large, heavy, and produce too little power (especially at high speed) for commercial use in a vehicle such as a car.
One problem associated with electrical machines, such as electric motors, is that it is necessary to cool them because they generate heat which reduces their efficiency. The need for optimization in cooling is even more important as increases in performance demands smaller packages. At present such machines may be cooled by blowing air through or over them. For heavy duty applications it is known to spray oil onto the rotor and stator assemblies and into the gap between them using a high pressure pump. A scavenger pump may also be provided to collect the sprayed oil for re-cycling.
A common configuration for such motors is to have an inner rotor mounted on a straight shaft supported by bearings on the ends. The bearings are mounted in end covers that support and locate the rotor in the center of a current-carrying stator. The rotor contains multiple current-carrying bars which run length wise parallel to the shaft and are located near the outer circumference of the rotor. Heat is produced in the rotor when the current in the stator excites the bars. Heat dissipation limits the design of the rotor. Another method used to dissipate heat is to pass oil coolant through a hollow rotor shaft, referred to as back iron cooling. Heat generated in the rotor conductor bars is dissipated into the core of the rotor, then into the rotor shaft and then into the oil coolant flowing through the shaft and exits the rotating machine to a heat exchanger. Although this cooling method has its advantages, such as simplicity in design, it is desirable to increase the amount of heat conduction away from the rotor bars of the motor and to concentrate the cooling at the source of the heat, namely, the rotor bars.